Separation of nickel and cobalt



United States Patent 2,971,836 SEPARATION OF NICKEL AND COBALT James D.Hall, 21811 Westehester Road, Shaker Heights, Ohio N Drawing. Filed Apr.29, 1957, Ser. N 655,479 12 Claims. (Cl. 75-419) The present inventionrelates to the chemistry of cobalt and nickel and is more particularlyconcerned with a novel process of making from cobalt-nickel aqueoussolutions cobalt compound precipitates containing over 99 percent of thecobalt contents of said solution and containing not in excess of 1.0percent of nickel.

The separation of cobalt from nickel where these ele ments exist insolutions as mixed salts is a classical problem in inorganic chemistry.However, this problem, unlike some other famous ones, is of substantialcommercial significance and in fact, its practical importance isincreasing constantly. Accordingly, the literature contains a number ofdisclosures of possible solutions to this problem, but to the best of myknowledge, prior to the present invention, there has never been known orused a method whereby separation of these two closely related elementsin aqueous salt solution could be accomplished satisfactorily in acommercial operation. Processes which would apparently or allegedlyenable quantitative separation in laboratory scale equipment have neverproven similarly efiective in commercial scale operations. On the otherhand, processes involving prohibitively high costs have been made towork in large scale use in the sense that they yielded cobalt and nickelproducts of good quality with respect to contamination by nickel orcobalt.

The method of my'present invention, which as indicated above, is freefrom the shortcomings and derelictions of the prior art and is adaptableto use upon any scale with uniformly satisfactory results. Thus, thepresent method is easyand inexpensive to carry out, involving relativelyfew steps and no complicated operations requiring expensive equipment orhigh labor costs because of special controls or skills required.Furthermore, product purity of both cobalt and nickel in terms not onlyof contamination by the other element of this pair, but of contaminationby other materials including reagents employed in the process, isuniformly high and depending upon the requirements of the manufactureror user of these products, may be adjusted easily to meet shiftingstandards or requirements Without complicating the process or addingmaterially to its expense. Surprisingly, the separations of thisinvention can be carried out effectively without regard to relativeamounts of cobalt and nickel in the original solution and withoutlimitation as to solution concentration. Thus large quantities of cobaltcan be removed from relatively small amounts of nickel in solution withthe same uniformly high purity product resulting as where the originalcobalt and nickel contents are approximately the same or where thenickel is present in far greater amount than the cobalt.

In addition to the foregoing advantages, the present method ofiers theoperator the choice of all the various soluble salts of nickel andcobalt as raw materials for the production of premium grade nickel andcobalt products. Similarly, this invention gives the operator a widechoice of reagents, and a certain amount of latitude in the choice ofproducts which he might obtain directly through the use of this method.The present method is also applicable advantageously to a broad range ofconcentrations of both cobalt and nickel. As a result, it is notnecessary to establish within reasonable limits any particular balancebetween cobalt and nickel salts in terms of relative or total quantitiesin a solution preliminary to beginning the processing of the solution inaccordance with this invention. These advantages sum up to an overalleconomic advantage of substantial importance be cause of the possibilityof the method being shifted in respect to raw materials, reagents, andproducts with market fluctuations.

The method of my present invention is predicated primarily upon mysurprising discovery of the critical effect which the pH of anickel-cobalt salt solution has upon the sharpness of the separation ofthese two elements from each other. I have found, in fact, that theoptimum pH condition for separating and removing cobalt from acobalt-nickel solution is about 2.4. In even large scale commercialoperations, practically quantitative removal of cobalt from such asolution can be expected where the pH is closely maintained throughoutat about 2.4. However, for most commercial purposes, a cobalt product ofacceptable grade for most purposes will be obtained where the pH of thesolution stands between about 1.8 and about 3.0 during the period ofprecipitation, separation and removal of the cobalt from the solution.In accordance with my present invention, as discussed more fully below,in my present regular commercial operations, solution pH is held withinthe range of about 2.0 to about 2.8 throughout the period of operationof this process.

Furthermore, I have-found that alkali hypochlorites, the heretoforeconventional reagents for this general purpose, cannot be used to securethe new results and ad vantages of this invention. In other words, it isessential to add chlorine and alkali independently and separately and tomaintain pH control as stated above throughout the period of the processthat cobalt is being precipitated.

I have also found that if the temperature of the solution at the timethat the cobalt product is precipitated and from that time on untilafter separation of the solid and liquid phases has been eflfected isbetween about 60 C. and 70 C., the removal of the cobalt product fromthe solution will be relatively quickly and easily accomplished. Bestresults in terms of ease and rapidity of separation of the two phasesare obtained toward the upper end of this range and accordingly, Iprefer to control the temperature during the operating period at about70 C.

In general, the method of this invention has as its basic object themaking of cobalt compounds of high purity, particularly with regard tonickel contamination, from solutions containing both cobalt and nickelin material amounts The making or preparing of these cobalt compounds inaccordance with this method is carried out in What amounts to a unitprocess, only a single reaction vessel and only a single reaction mediumbeing required for consistently satisfactory results. Thus this methodcomprises in its broadest aspects the steps of bringing chlorine into asolution containing cobalt and nickel so as to saturate the solutionwith chlorine and thereby reduce its pH from not more than about 3.0 toless than about 2.0 while the solution temperature is maintained betweenabout 30 C. and about C., introducing an alkali into the solution,discontinuing the introduction of chlorine and alkali into the solutionwhen the cobalt content of the solution has been substantiallyexhausted, and then separating and removing from the resulting liquidphase the solid phase containing cobalt compounds substantially freefrom nickel contamination.

Aqueous cobalt-nickel solutions suitable for use in the method of thisinvention are those containing more than about 1.0 percent of cobalt inwhich the cobalt and nickel are in the ratio of from one part of cobaltper ten parts of nickel to ten parts of cobalt per one part of nickel.Maximum cobalt and nickel concentrations of these solutions may at leastin theory be the upper limits of solubility of the particular cobalt andnickel compounds contained in the solutions. In other words, the resultsof this invention can be secured over essentially the full range ofsolution concentration of cobalt and nickel compounds although, as thoseskilled in the art will recognize, for practical and commercialoperations the cobalt compound concentration in the solutions should lieintermedlately in this theoretical range and I prefer that the cobaltconcentration be relatively high for maximum yields of high-puritycobalt products. If a high-purity nickel product is an object, I preferthat the solution initially contain relatively large quantities ofnickel compounds for the same reason] However, an important advantage ofthis invention is that whether it is premium cobalt or nickel productsthat are desired, the method can be appliedto virtually any aqueouscohalt-nickel solution simply by following the same basic procedure asis used in treating ideal or specially preferred types of solutions.

The step of bringing elemental chlorine into the solution is carried outpreferably by bubbling chlorine ga into the solution in a suitablereaction vessel and this is done after the pH of the solution has beenchecked and adjusted if necessary to bring it down to not more thanabout 3.0. In theory, chlorine might be used to make this initial pHadjustment where the solution is more alkaline than pH 3.0, but thiswould be an expensive way to operate when sulphuric acid, for example,is available for the purpose at costs far below the least expensive formof chlorine. Furthermore, the purpose of adding chlorine in accordancewith this invention is to saturate the solution with chlorine and thisis accomplished by dropping the pH solution from not more than about 3.0to less than about 2.0, suitably 1.5 to 1.8. .The solubility of chlorinein the solution will depend to a large extent upon the temperature ofthe solution.

In theory again, the solution temperature may range between 30 C. and 95C., but I prefer that it lie between 60 C. and 70 C. The disadvantage oftemperatures approaching the boiling point temperature of the solutionis that chlorine solubility is very limited and chlorine losses maythereforebe excessive without any offsetting advantage such assubstantial increase in reaction rate or the production of a more easilyfiltered cobalt product precipitate. The temperatures in the lowerportion of this range on the other hand lead to the production of cobaltprecipitates which are gelatinous or slimy and difiicult to separate andwash free from the reaction liquor and again there is no offsettingadvantage such as an increased reaction rate or reduced chemical costs.

There is a certain flexibility in respect to the sequence of thepreliminary steps of pH adjustment prior to chlorine saturation of thesolution and adjustment of the solution temperature by either a heatingor a cooling operation. Either or both of these adjustments may be made,in other words, at the same time or in sequence in accordance with theoperators preference. Furthermore, as suggested above these adjustmentsmay both or either be made after the chlorine is first contacted withthe solution. The important consideration in this respect is themaintenance of the critical pH in the re action mixture over as much ofthe cobalt precipitation separation and removal periods as possible.This im plies the establishment of the critical initial pH as the firststep or at least as an early step in the present 4 method and beforechlorination has been'carried very far.

The temperature factor, while not nearly so critical as pH from thestandpoint of product purity, is important commercially because itsproper in accordance with this invention assures the production of aprecipitate which lends itself to rapid and clean, separation from theliquid phase. For best results, the adjudstment of reaction solutiontemperature should be made at the outset and before chlorination has progrossed to the point that substantial amounts of cobaltic hydroxide arebeing formed and precipitated,

Also, in accordance with my preference, the introduction of the chlorineis accomplished by bubbling chlorine gas into the solution at aplurality of locations in the vessel containing this solution in orderto assure relatively uniform distributcn of chlorine and its oxidizingeffects. Likewise, the alkali is continuously introduced into thesolution at a plurality of locations and to aid in keeping the solutionpH uniform throughout the base is used in the form of a relativelydilute aqueous solution. The chlorine and alkali solution are normallyadded to the cobalt and nickel salt solution simultaneously and atpredetermined related rates to assure maintenance of the solution pHwithin the aforesaid range, but additions of one or the other may betemporarily increased or decreased in rate or discontinued in order toadjust the pH as necessary in accordance with my discovery set forthabove.

While in general, any alkali may theoretically be employed to establishand maintain the critical pH range in the solution of mixed salts whilethe process of this invention is carried out, I prefer to use an aqueoussolution of an alkali metal hydroxide and because of economic reasons, Inow employ, in commercial operations, either an aqueou 50 percentsolution of caustic soda or an aqueous 20 percent solution of soda ash.Any hydroxide or carbonate (including bicarbonates) of an alkali metalor an alkaline earth metal may be used for this purpose. However,calcium hydroxide and calcium carbonate and the corresponding compoundsof barium, magnesium, and strontium and related compounds of alkalinecharacter are generally of relatively little pratical interest in thisinvention process. Thus, where the salt solution is composed ofsulfates, I do not use a calcium compound for pH adjustment or controlbecause of the difliculty of preventing calcium sulfate contaminatlon ofthe final desired product. The problems which magnesium compoundspresent in terms of both cobalt product and nickel product purity are sosubstantial as to preclude the possibility of their use in mostcommercial operations at the present time. Compounds of lithium, barium,and strontium of this class, in addition to presenting problems incommon with calcium or magnesium compounds, are normally too expensiveto be employed in commercial operations of this type.

Potassium hydroxide and potassium carbonate, aside from the presentlyunfavorable economic picture, are quite satisfactory for use inaccordance with this invention, particularly where the cobalt and nickelsalts are sulfates.

Sodium and potassium silicates qualify in theory as alkalis for thepresent purpose but are not desirable here because of their cost and thefact that they could lead to contamination of the cobalt and/ or nickelproducts. The same may also be true of other salts of strong bases andweak acids. In any event, these alkaline substances do not representeither my preferred practice or a presently commercially feasiblealternative to that practice.

Normally, the precipitation of cobalt in a plant operation will becomplete within about 1% to 3 hours. I have found, in fact, in myordinary commercial production, that for all practical purposes, it isnot necessary to chlorinate the solution more than 2 /2 hours. However,those skilled in' the art will understand that this use and control pperiod will vary depending upon the efficiency with which the chlorineis used and distributed through the reaction mixture. They will alsounderstand that it is possible quickly to determine the condition of thesolution with respect to cobalt content at any time so that thechlorinaion step may be discontinued just as soon as cobalt oxidation iscomplete. It may be found desirable in the larger installations tofollow closely the course of the cobalt oxidation reaction andprecipitation in order to conserve time and reagents.

Since as stated previously and emphasized in the appended claims, it isimportant in accordance with this invention to selectively precipitatecobalt compounds from nickel-cobalt solutions and to do thisprogressively, it is essential to regulate the rates of addition ofchlorine and alkali to the reaction solution throughout the cobaltprecipitation period. It is also important to regulate the proportion ofchlorine to alkali during the various stages of the cobalt precipitationperiod. When there is a substantial quantity of cobalt in solution, asat the outset of the chlorination of a relatively strong cobaltsolution, the alkali-chlorine ratio may be relatively high. As theamount of cobalt in solution is diminished and the solution pHaccordingly begins to climb toward 3.0, the alkali-chlorine ratio issubstantially reduced, typically to about half the initialalkali-chlorine ratio. Then later, as the end-point of cobaltprecipitation is closely approached, the proportion of alkali tochlorine will again be diminished finally to the point where no alkalior virtually no alkali is being introduced into the reaction mixture aschlorination continues. This, however, does not mean or imply that thealkali and the chlorine must be added simultaneously throughout thecobalt precipitation period, or that they must be added at adjacentpoints in the solution, or that they might in any way be premixed andadded together to the solution. 0n the contrary, the alkali and chlorinemay be added intermittently or alternately throughout the cobaltprecipitation period or during any part thereof, and they may beintroduced into the reaction vessel at widely spaced points. In no case,however, should they be premixed with each other for addition togetheror as alkali hypochlorite or other reaction product.

The course of the cobalt precipitation operation and reactions involvedtherein can be followed closely by means of a standard pH machine whichelectrically and practically instantaneously determines the pH of thesolution, as those skilled in the art know and understand. Through theuse of this machine or meter, the operator can adjust the rates ofalkali and chlorine additions and can establish the requiredalkali-chlorine ratios and adjust these ratios or proportions from timeto time in order to maintain close control over the cobalt precipitationand thereby progressively and selectively precipitate greater than 99percent of the original cobalt content of the starting cobalt-nickelsolution. Those slc'lled in the artwill further understand that becauseof the flexibility of this process and the opportunity for choice of theoperator as to not only the rate of the cobalt precipitation operationbut also the timing of the alkali and chlorine additions and theparticular pH control points along the course of the cobaltprecipitation period, it is not necessary or possible in fact toestablish a particular inflexible set of conditions for the entireoperation or for any given increment of the whole period within thegeneral ranges, ratios, and rates set out above. Thus, for example, in asequential or alternate alkali-chlorine addition operation in accordancewith this invention process, one operator may add only alkali andanother may add only chlorine, and still another may add chlorine andalkali in rigidly controlled ratio over one relatively long portion ofthe cobalt precipitation period.

When the predetermined end point of cobalt concentration in the saltsolution has been reached, chlorination is discontinued, the supply ofbase is cut oil, and the re suiting solid and liquid mixture is thenstirred for a period of from 5 minutes to 1 hour, according tothe'degree of control exercised over solution pH during chlorina tionand the quality of the products required. This agitation of the mixturehas the efliect of increasing the purity of the products by the physicalmeans of bringing about better contact between the precipitate and themother liquor and assuring uniformity of pH and other conditionsthroughout the mixture. A certain small amount of nickel hydroxide whichmay have been precipitated with the cobalt because of a local variationin pH outside the permissible range will thus be redissolved, andsimilarly any unprecipitated cobalt will be oxidized and dropped fromthe solution where previously a local condition permitted it to remainin soluble form.

If desired, the mixture may be blown with air to exhaust substantiallyall residual dissolved chlorine.

The final step of separating the precipitated cobaltic hydroxide fromthe resulting solution rich in high-grade nickel salt may be carried outin any suitable manner, depending upon the operators desires and theequipment available. Providing the precipitate is of loose, granularcharacter, filtration will usually be preferred in effecting thisseparation. Where the temperature control has not been such during theprecipitation period that the cobalt product may be easily filtered, acontinuous centrifuge operation may be carried out. Alternatively, thecobalt product may be separated by decantation with the usual sequenceof rinsing steps to assure clean separation. However, in any event, itis important that the pH of the mother liquor as well as the pH of allrinsing or washing solutions be within the range specified above andpreferably near 2.4.

Cobalt-nickel solutions useful in the process of this invention are,generally speaking, those which contain primarily only cobalt and nickelcompounds or salts in substantial quantities, i.e. in excess of about1.0 percent of each said metal. Solutions that have proven particularlywell suited for treatment by this process were those obtained throughthe digestion of high-temperature cobalt alloys by the methods disclosedand claimed in my United States Patent No. 2,716,588, granted August Intypical commercial operations under that patent, the ultimatecobalt-nickel solution after removal of iron, chromium and manganese isa cobalt sulfatenicke-l sulfate solution of pH normally somewhat above3.0, as between 4.0 and 5.0. However, this solution may suitably consistof the acetates, formates, fluorides, chlorides, phosphates, or nitratesof cobalt and nickel. There is no variation required in the method ofthis invention to accommodate any of these various compositionpossibilities of the initial cobalt solution and this is a furthersubstantial advantage of this invention.

Those skilled in the art will gain further and better understanding ofthis invention on consideration of the following illustrative, but notlimiting, examples of the present method:

Example I Two thousand gallons of a solution obtained through thepractice of my inventions disclosed and claimed in my said United Statespatent were filtered in standard filter press, separating compounds ofiron, chromium, and related elements in solid phase from dissolvedcobalt and nickel values. The pH of this solution being relatively high,sulfuric acid was added in sufficient amount to bring the pH to about2.4. This solution was then heated to bring its temperature to 70 C. andthe introduction of chlorine in the form of bubbles of gas was begun.Substantially simultaneously aqueous caustic soda of 50 percent strengthwas dribbled into the solution at a predetermined rate necessary tomaintain the pH within the standard separating range of 2.0 to 2.9.After 2 hours of'continuous chlorination under these conditions, withcontinuous agitation for better mixing, substantially all the cobalt hadbeen precipitated in the form of cobaltic hydroxide. Chlorination wasthen stopped, as also was the introduction ofcaustic soda, and themixture was agitated for a period of ten minutes and at the same timeblown. with air to eliminate residual dissolved chlorine to a largedegree. Separation of the solid phase from the liquid was accomplishedby conventional filter press means with the result that the filtrateanalyzed 0.75 percent cobalt (expressed as metal) and the cobalt productcontained 0.75 percent nickel (also expressed as metal).

Example 11 Another solution obtained through the practice of myinventions disclosed and claimed in my aforesaid patent was treated in atotal volume of 2000 gallons containing 280 pounds of cobalt (calculatedas metal) and 140 pounds of nickel (also calculated as metal). Afterremoval of compounds of chromium, iron and manganese, sulphuric acid wasadded to bring the solution pH to 3.0. The solution temperature wasadjusted to 60 C. and chlorine was then bubbled into the solutioncontained in a corrosion resistant reactor vessel. An aqueous 20 percentsolution of soda ash was dribbled into the vessel after the chlorine gashad been turned on and adjusted and for a period of several minutes astrong odor of chlorine is noted over the reaction mixture. The chlorineodor then faded and the pH ultimately dropped to 1.5, and

.then while the ratio of chlorine and soda ash was maintained constantthe pH began to climb slowly. The solution at the minimum pH reading wassaturated with chlorine. The course of the reactions involved in thisprocess was followed by means of a pH machine and the ratio of chlorineand soda ash solution and the rates of introduction of chlorine and sodaash were adjusted to maintain the pH between about 2.0 and about 2.4.After about one hour during which the ratios of chlorine and soda ashand the rates of addition of these materials to the solution weremaintained constant, the pH started upward abruptly and at the same timelightening of the color of the solution from black to dark brownish wasnoted. The addition of soda ash solution was then cut back gradually andthe original black color returned as the pH fell back and steadied atbetween 2.2 and 2.4. A new reduced ratio of soda ash to chlorine wasthus established to maintain this pH condition and in a short time thecolor of the solution began to change through reddish brown to red andthen to a lighter and clearer appearance. The pH meanwhile remainingbetween 2.2 and 2.4. Containing the additions of soda ash and chlorinein the immediately previously established ratio, the pH of the solutiongradually rose to 2.6 to 2.8 as the solution turned greenish in color,whereupon the rate of alkali addition was again cut back substantiallywhile the rate of chlorine addition was maintained at the originallevel. The purpose of this alteration in the alkali-chlorine ratio wasto maintain the solution pH below about 3.0 and thereby preventprecipitation of nickel compounds. The last traces of cobalt wereextracted from the solution at this stage and again a strong odor ofchlorine was noted. The pH of the solution thus shows a tendency toclimb as the cobalt is precipitated from the solution and this tendencybecomes more noticeable as the amount of cobalt content of the solutionapproaches exhaustion. Accordingly, during the final cobaltprecipitation stage the soda ash was added only very sparingly andslowly to the solution and when the pH of the solution exceeded 3.0 thealkali addition was stopped entirely. At this point with chlorine stillbubbling into the solution a marked frothing effect was observed on thesurface of the reaction mixture. The chlorine was then shut off and themixture filtered to separate the precipitated cobaltic hydroxide fromthe nickel solution which was thereafter treated for the precipitationand recovery of nickel. The

procedure used in precipitating nickel from the solution. comprisedadding'more soda ash solution to bring the pH' to 7.8 to 8.0 while thesolution temperature is maintained at between 60 C. and 70 C. I e

The cobaltic hydroxide upon analysis contained 0.9 percent nickel(calculated on the metal basis) and the nickel product contained 0.9percent cobalt (also on the metal basis). This was well within thespecifications for both these materials and represented a premium cobaltand nickel and a highly satisfactory commercial operation in terms ofyields as well as purity.

Example III In still another operation involving the use of solutionsobtained through the practice of my aforesaid patent processes, theinitial solution of 2000 gallons of liquor containing 375 pounds ofnickel to 42 pounds of cobalt as the sulphates was treated in accordancewith the present method with recovery of high purity products of cobaltand nickel. In this case the solution temperature approximated 50 C.throughout the reaction period and the alkali employed was sodiumcarbonate which was added as a 20 percent aqueous solution beginningafter the solution was saturated with chlorine, which was bubbled in thereaction vessel containing the solution through a manifold having anumber of separate spaced openings. The chlorine and alkali were addedat sep' arate ends of the reaction vessel but, as in Examples 1 and II,the reactions mixture was constantly agitated throughout the reactionperiod to assure uniform conditions and results. Also as in theforegoing operations, the ratio of alkali and chlorine was establishedat the outset by using the solution pH as a guide and following changesin the solution acidity as the reactions continued. The changes in theratio of alkali to chlorine were made as before as the end point ofcobalt removal was approached in stages. Following the removal of thecobalt from the solution, a phase separation was carried out to removethe cobaltic hydroxide from the reaction liquor which in turn wassubsequently treated for the removal of nickel. Again, the yieldsofcobalt and nickel were excellent as was the purity of each product interms of the other. Cobalt recovery was over 99 percent of theoreticaland the cobalt product contained 0.9 percent nickel (calculated asmetal) and the nickel product contained 0.9 percent cobalt (on the samebasis).

Example IV In another operation in accordance with this invention usinga cobalt-nickel solution of the composition of the solution of Example111 and generally the same procedure, the additions of chlorine andalkali may be made intermittently throughout the cobalt precipitationperiod. In this case the solution is saturated with chlorine and thechlorine-alkali ratio is established by following the course of thecobalt precipitation reactions with a pH machine and additions ofchlorine and alkali are discontinued at intervals. Adjustments in therates of the chlorine and alkali additions and the proportions of alkaliand chlorine added are made as the cobalt precipitation proceeds asrequired at check points along the course of the cobalt precipitationperiod. Thus as in the case of the continuous addition of chlorine andalkali as set out in Examples 11 and Ill above, for instance, an initialratio of chlorine and alkali is established and this is altered when thepH reaches 2.0 to 2.4 and the amount of cobalt remaining in solution isdiminished to the point that the solution color and clarity isnoticeably changed. Again, the chlorine-alkali ratio is altered justbefore the last of the cobalt is precipitated from the solution in orderto prevent the pH of the solution from rising above about 3.0 and toprevent precipitation of nickel to contaminate the cobalt precipitate.

Example V Following the procedure of Example IV and using the sameinitial solution, the temperature of the solution may be ad usted toabout 35 C. before chlorine is introduced therein. This temperature thenmay be maintained throughout the cobalt precipitation period. In thisoperation an aqueous 7 percent solution of sodium bicarbonate is thealkali and chlorine is again introduced as a gas into the solution bymeans of a manifold having a number of outlets in the reaction vesselbelow the solution surface. The cobalt precipitate in this case isgelatinous, slimy, and difiicult to separate from the solution anddiflicult to wash free from all traces of nickel. Decantation may beemployed as the first step and the precipitate may be washed bydecantation technique and then finally filtered and washed again.

Example VI In another opera ion quite like that of Example III, asolution temperature may be initially adjusted to about 95 C. andmaintained at substantially that level through out the cobaltprecipitation period. Chlorine gas will again be introduced through amanifold into the solution and a 50 percent aqueous solution ofpotassium hydroxide will be employed as the alkali. The cobaltprecipitation product will be separated suitably for filtration from thereaction liquor and washed and a high yield of premium grade cobalthydroxide obtained.

I do not prefer to employ superatmospheric pressures or to apply vacuumsto the reaction vessels during the cobalt precipitation period of thepresent process. Those skilled in the art will understand, however, thatwhere the operator desires he may apply pressure or vacuum in carryingout this invention and thereby alter the outer limits of temperature setforth above. Such variations of thepresent process are contemplated bythe ap ended claims although, as stated above, the optimum condition foroperation of this process so far as temperature is concerned is in therange of 60 C. to 70 C., this being the temperature interval in whichbest results are obtained in terms of a granular, easily-filterablecobalt precipitate.

This application is a continuation-in-part of my prior application,Serial No. 441,669, filed July 6, 1954, now abandoned.

Having thus described this invention in such full, clear,

concise and exact terms as to enable any person skilled in the art towhich it pertains to make and use the same, and having set forth thebest mode contemplated of carrying out this invention, I state that thesubject matter which I regard as being my invention is particularlypointed out and distinctly claimed in what is claimed, it beingunderstood that equivalents or modifications of, or substitutions for,parts of the above specifically described embodiments of the inventionmay be made without departing from the scope of the invention as setforth in what is claimed.

What is claimed is:

l. The method of making from an aqueous cobalt-nickel solutioncontaining more than about 1.0 percent of cobalt in which the cobalt andnickel are in the ratios of from one part of cobalt per ten parts ofnickel to ten parts of cobalt per one part of nickel, a cobalt compoundprecipitate representing over 99 percent of the initial cobalt contentof the solution and containing not in excess of 1.0 percent of nickel,which comprises the steps of bringing chlorine gas into the solution andsaturating said solution with chlorine and thereby reducing its pH fromnot more than about 3.0 to less than about 2.0 while the temperature ofthe solution is maintained between about 30 C. and about 95C.,introducing into the solution an alkali, finally discontinuing theintroduction of chlorine and said alkali when the cobalt content of thesolution has been substantially exhausted and separating and removingfrom the resulting liquid phase the solid phase containing cobaltcompounds free from nickel contamination in excess of 1.0 percent.

2. The method of making from an aqueous cobalt-nickel solutioncontaining more than about 1.0 percent of cobalt in which the cobalt andnickel are in the ratios of from one part of cobalt per ten parts ofnickel to ten parts of cobalt per one part of nickel, a cobalt compoundprecipitate, representing over 99 percent of they initial cobalt contentof the solution and containing not in excess of 1.0 percent of nickel,which comprises the steps of bringing chlorine gas into the solution andsaturating said solution with chlorine and thereby reducing its pH fromnot more than about 3.0 to less than about 2.0 while the temperature ofthe solution is maintained between about 60 C. and about C., introducingan alkali into the solution as soon as the solution has been saturatedwith chlorine, simultaneously adding chlorine and said alkali to thesolution, finally discontinuing the introduction of chlorine and saidalkali when the cobalt content of the solution has been substantiallyexhausted and before substantially any nickel has been precipitated, andseparating and removing from the resulting liquid phase the solid phasecontaining cobalt compounds free from nickel contamination in excess of1.0 percent.

- 3. The method of making from an aqueous cobalt-nickel solutioncontaining more than about 1.0 percent of cobalt in which the cobalt andnickel are in the ratios of from one part of cobalt per ten parts ofnickel to ten parts of cobalt per one part of nickel, a cobalt compoundprecipitate representing over 99 percent of the initial cobalt contentof the solution and containing not in excess of 1.0 percent of nickel,which comprises the steps of bringing chlorine gas into the solution andsaturating said solution with chlorine and thereby reducing its pH fromnot more than about 3.0 to less than about 2.0 while the temperature ofthe solution is maintained between about 60 C. and about 70 C.,introducing an alkali into the solution after the solution has beensaturated with chlorine, intermittently adding chlorine and said alkalito the solution, finally discontinuing the introduction of chlorine andsaid alkali when the cobalt content of the solution has beensubstantially exhausted and before substantially any nickel has beenprecipitated, and separating and removing from the resulting liquidphase the solid phase containing cobalt compounds free from nickelcontamination in excess of 1.0 percent.

4. The method of making from an aqueous cobaltnickel solution containingmore than about 1.0 percent of cobalt in which the cobalt and nickel arein the ratios of from one part of cobalt per ten parts of nickel to tenparts of cobalt per one part of nickel, a cobalt compound precipitaterepresenting over 99 percent of the initial cobalt content of thesolution and containing not in excess of 1.0 percent of nickel, whichcomprises the steps of bringing chlorine gas into the solution andsaturating said solution with chlorine and thereby reducing its pH fromnot more than about 3.0 to less than about 2.0 while the temperature ofthe solution is maintained between about 60 C. and about 70 C., startingintroduction of soda ash into the solution while the solution issaturated with chlorine, finally discontinuing additions of chlorine andsoda ash to the solution when the cobalt content of said solution hasbeen substantially exhausted and before substantially any nickel hasbeen precipitated, and separating and removing from the resultingsolution the solid phase containing cobalt compounds free from nickelcontamination in excess of 1.0 percent.

5. The method of making from an aqueous cobaltnickel solution containingmore than about 1.0 percent of cobalt in which the cobalt and nickel arein the ratios of from one part of cobalt per ten parts of nickel to tenparts of cobalt per one part of nickel, a cobalt compound precipitaterepresenting over 99 percent of the initial cobalt content of thesolution and containing not in excess of 1.0 percent of nickel, whichcomprises the steps of bringing chlorine gas into the solutionandsaturating said solution with chlorine and reducing its pH from not morethan about 3.0 to less than about 2.0 while the temperature of thesolution is maintained at about 63 C., bringing caustic soda into theresulting chlorine-saturated solution, adding chlorine and caustic sodaseparately to the said solution at rates and in proportions to eachother such that cobalt is substantially continuously precipitated fromthe solution while nickel is retained in solution, finally discontinuingadditions of chlorine and caustic soda when the cobalt content of thesolution has been substantially exhausted and before substantially anynickel has been precipitated, and separating and removing from theresulting solution the solid phase containing cobalt compounds free fromnickel contamination in excess of 1.0 percent.

6. The method of making from an aqueous cobaltnickel solution containingmore than about 1.0 percent of cobalt in which the cobalt and nickel arein the ratios of from one part of cobalt per ten parts of nickel to tenparts of cobalt per one part cf nickel, a cobalt compound precipitaterepresenting over 99 percent of the initial cobalt content of thesolution and containing not in excess of 1.0 percent of nickel, whichcomprises the steps of bringing chlorine gas into the solution andsaturating said solution with chlorine and reducing its pH from not morethan about 3.0 to less than about 2.0 while the temperature of thesolution is maintained between about 30 C. and about 95 selected fromthe group consisting of hydroxides and carbonates of alkali metals andalkaline earth metals into the resulting chlorine-saturated solution,separately adding chlorine and said alkali to said solution at rates andproportions to each other etfective to progressively and selectivelyprecipitate cobalt from the solution while the nickel is retained insolution, finally discontinuing additions of chlorine and said alkaliwhen the cobalt content of the solution has been substantiallyexhausted, and separating and removing from the resulting solutioncobalt compound precipitate free from nickel contamina tion in excess of1.0 percent.

7. The method of making from an aqueous cobaltnickel solution containingmore than about 1.0 percent of cobalt in which the cobalt and nickel arein the'ratios of from one part of cobalt per ten parts of nickel to tenparts of cobalt per one part of nickel, a cobalt compound precipitaterepresenting over 99 percent of the initial cobalt content of thesolution and containing riot in excess of 1.0 percent of nickel, whichcomprises the steps of bringing chlorine gas into the solution andsaturating said solution with chlorine and thereby reducing its pH fromnot more than about 3.0 to less than about 2.0 while the temperature ofthe solution is maintained between about 30 C. and about 95 C.,introducing soda ash into the solution, bringing additional amounts ofchlorine and soda ash into said solution and thereby progressivelyselectively precipitating cobalt from the solution while the nickel isretained in solution, finally discontinuing the introduction of chlorineand said alkali when the cobalt content of the solution has beensubstantially exhausted, blowing air into the solution untilsubstantially all the chlorine thereby releasable from the solution hasbeen eliminated from said solution, and separating and removing from theresulting liquid phase the solid phase containing cobalt compounds freefrom nickel contamination in excess of 1.0 percent.

8. The method of separating cobalt from an aqueous solution containingnickel and cobalt salts which comprises the steps of introducingchlorine into the solution, adding an alkali metal hydroxide to thesolution to maintain the pH between about 1.8 and about 3.0,discontinuing the addition of chlorine and said hydroxide to thesolution when precipitation of cobaltic hydroxide has substantiallyceased, and separating and removing the resulting solid phase containingcobaltic hydroxide from C., bringing an alkali 12 the liquid phasecontaining nickel substantially free from cobalt contamination.

9. The method of separating cobalt from an'aqueous sulfuric acidsolutioncontaining nickel and cobalt salts which comprises the steps ofadding an alkali metal hydroxide to the solution pH to a value of about2.4, heating the solution and bringing its temperature to about C., thencontinuously bubbling chlorine into said solution, continuously runningaqueous caustic soda into the solution to maintain the pH between about2.0 and about 2.8, discontinuing the additions of chlorine and causticsoda to the solution when precipitation of cobaltic hydroxide hassubstantially ceased, stirring the resulting solid and liquid mixture,and separating and removing the solid phase containing cobaltichydroxide from the liquid phase containing nickel substantially freefrom cobalt contamination.

10. A one-stage process of separating cobalt and nickel values from asolution of their salts, which consists substantially of simultaneouslyadding chlorine and a material from a group consisting of alkali metaland alkalineearth metal carbonates to the solution in a ratio suflicientto maintain the pH initially between about 2 and 3 thereby precipitatingmore than 98% of the cobalt contained in the solution as a hydroxidewhile the nickel remains in solution, and rapidly separating thesubstantially pure precipitated cobalt hydroxide from the solution toprevent absorption of nickel.

11. The method of separating cobalt from an aqueous solution containingnickel and cobalt salts which comprises the steps of heating thesolution to a temperature of between about 60 C. and about 70 C.,introducing chlorine into the thus heated solution, adding to thesolution a material selected from the group consisting of alkali-metaland alkaline-earth metal carbonates to the solution in a ratiosufficient to maintain the pH be tween about 1.8 and about 3.0,discontinuing the addition of chlorine and said material whenprecipitation of cobaltic hydroxide has ceased and separating andremoving the resulting solid phase containing cobaltic hydroxide fromthe liquid phase containing nickel substantially free from cobaltcontamination.

12. The method of separating cobalt from an aqueous solution containingnickel and cobalt salts which comprises the steps of heating thesolution to a temperature between about 60 C. and about 70 C.,continuously bubbling chlorine into the solution, continuously runninginto the solution a material selected from the group consisting ofalkali metal and alkaline-earth metal carbonates in a ratio sufiicientto maintain the pH between about 1.8 and about 3.0, discontinuing theaddition of chlorine and said material when precipitation of cobaltichydroxide has substantially ceased and separating and removing theresulting solids phase containing cobaltic hydroxide from the liquidphasecontaining nickel substantially free from cobalt contamination.

References Cited in the file ofthis patent UNITED STATES PATENTS2,367,239 Renzoni Jan. 16, 1945 2,377,832 Wallis et al. June 5, 19452,694,005 Schaufelberger Nov. 9, 1954 2,728,636 Van Hare et al. Dec. 27,1955 2,778,728 Roy et a1 Jan. 22, 1957 FOREIGN PATENTS 755,044 GreatBritain Aug. 15, 1956 775,788 Great Britain May 29, 1957

8. THE METHOD OF SEPARATING COBALT FROM AN AQUEOUS SOLUTION CONTAININGNICKEL AND COBALT SALTS WHICH COMPRISES THE STEPS OF INTRODUCINGCHLORINE INTO THE SOLUTION, ADDING AN ALKALI METAL HYDROXIDE TO THESOLUTION TO MAINTAIN THE PH BETWEEN ABOUT 1.8 AND ABOUT 3.0,DISCONTINUING THE ADDITION OF CHLORINE AND SAID HYDROXIDE TO THESOLUTION WHEN PRECIPITATION OF COBALTIC HYDROXIDE HAS SUBSTANTIALLYCEASED, AND SEPARATING AND REMOVING THE RESULTING SOLID PHASE CONTAININGCOBALTIC HYDROXIDE FROM THE LIQUID PHASE CONTAINING NICKEL SUBSTANTIALLYFREE FROM COBALT CONTAMINATION.